Sulfopozzolanically active fly ash and composition

ABSTRACT

A new bituminous coal fly ash is sulfopozzolanically reactive and contains combined sulfate in stated proportions relative to alkaline earth metal oxide content. Load-supporting compositions of this fly ash combined with aggregate, and a method of applying the new fly ash to an existing surface.

AU 112 EX 72] Inventor Leonard John Minnick Cheltenham, Pa. [21 Appl.No. 780,902 [22] Filed Dec. 3, 1968 [45] Patented Jan. 11, 1972 [73]Assignee G. & W. H. Corson Inc.

Plymouth Meeting, Pa.

[5 4] SULFOPOZZOLANICALLY ACTIVE FLY ASH AND COMPOSITION 12 Claims, NoDrawings [52] (1.8. Ci 106/85, 106/97, 106/287 SS, l06/DlG. l [51] Int.Cl C04b 7/12 [50] Field of Search 106/85, 97, DIG.- 7, 287; 23/178 [56]References Cited UNITED STATES PATENTS 3,475,121 10/1969 Thornton 23/1783,320,906 5ll967 Domahidy 23/l78 2,987,408 6/1961 Minnick 106/85 OTHERREFERENCES Simons and Jeffery, An X-ray Study of Pulverized Fuel Ash,"J. Appl. Chem. 10, Aug. 1960, pp. 328- 336.

Minnick, L. John, Reactions of Hydrated Lime with Pulverized Coal FlyAsh," complete article, apparently published about Mar. 15, 1967.

Primary Examiner-Tobias E. Levow Assistant Examiner-W. T. Scott Anomey-Paul & Paul SULFOPOZZOLANICALLY ACTIVE FLY ASH AND COMPOSITION BRIEFSUMMARY OF THE INVENTION BACKGROUND OF THE INVENTION The patents toHavelin and Kahn US. Pat. Nos. 2,564,690, 2,698,252, 2,815,294, and2,937,581 disclose compositions and methods for forming stabilizedload-supporting bases such as roads, highways, airport runways and thelike. Those patents disclose various combinations of lime and fly ashwith other ingredients such as soil, sand, clay, and the like. Otherpatents of the group disclose the addition of ingredients such asspecially graded aggregate and the like.

The patent to Minnick et al. U.S. Pat. No 3,206,319 discloses animproved form of fly ash, and indicates the nature of various effortsthat have been made in the industry relating to the stabilization ofload-supporting bases.

One of the important factors in providing a stabilized loadsupportingbase is to provide a composition which sets up sufficiently rapidly thatit possesses a relatively high early compressive strength. Ordinary flyash, collected from the usual precipitators in the stacks of coalburning furnaces, produces a stabilized soil composition which sets uprather slowly and requires many weeks of time in order to build up ahigh compressive strength.

The primary difficulty with these materials, as noted in theaforementioned patents, is concerned with the rather slowrate ofhardening which is characteristic of these compositions. Directlyassociated with this situation are problems related to durability underalternate cycles of wetting and drying or freezing and thawing. Delaysare sometimes experienced in construction while adequate structuralcharacteristics are developed in the compositions.

It is an object of this invention to provide a specially prepared flyash which has excellent properties when used in compositions of the typereferred to. Further, the invention relates to load-supportingcompositions having relatively high early compressive strength, andwhich contain such novel fly ash. Still another object is to provide amethod of making such highly active fly ash.

Recent investigations have indicated that dolomite and high calciumlimestones offer some possibility in the treatment of gases containingsulfur oxides as produced in the combustion of coal and oil. The effortto data has been primarily concerned with the injection of the rawlimestone (calcite or dolomite, for example) into the fuel or into thefurnace so that the high temperature of burning calcines the limestoneto form an oxide or mixture of oxides which in turn reacts with thesulfur trioxide and sulfur dioxide in the gas. Unfortunately, theattempts to accomplish this have been largely unsuccessful in thatsubstantially higher amounts of limestone are required than thestoichiometric requirement to react with the sulfur oxides. This,therefore, requires high doses of the additive which presents bothphysical difficulties in the injection process (contaminates the boiler)and economic disadvantages. Furthermore, the fly ash product of theseattempts has always contained very little of the sulfur in the form ofsulfate. Some attempts have been made to treat the resulting ash whilesuspended in the gas stream in scrubbers, the purpose of this being tohydrate the lime and thereby capture any residual sulfur dioxide. Such aprocess results in the formation of substantial quantities of calciumand/or magnesium sulfite which are well known to be toxic and are alsoobjectionable from the standpoint of their utilization in compositionssuch as mortar, concrete and the like.

SUMMARY OF THE INVENTION It has now been discovered that excellentload-supporting compositions may be prepared from a novel highly active,sulfopozzolanically reactive fly ash, which is useful per se, or as acomponent in compositions in the ranges which follows:

Z by weight Highly uctive fly ash 8 to Aggregate 5 to 87 Water 5 lo 30The highly active fly ash according to this invention has a combinedsulfur content of about 5 to 50 percent expressed as sulfur trioxide,and a content of calcium oxide plus magnesium oxide (actually present asthese compounds) from about 0.5 to about 30 percent by weight, whereinthe ratio of uncombined calcium oxide plus magnesium oxide to combinedcalcium oxide plus magnesium oxide varies from about 0.2:] to about 3:1.The sulfur content includes substantial concentrations of sulfate ionsin combination with calcium oxide and magnesium oxide, as well as otherconstituents of the ash. Specifically the preferred compounds that arepresent include calcium sulfoaluminates of several types, calcium andmagnesium sulfates, as well as certain complex silicates. It issignificant that the calcium oxide and magnesium oxide content is in amineralogical form that provides special characteristics which obviatethe undesirable effect that such oxides produce in a fly ash and furtherenhance the properties of the ash so that when used in certaincompositions the ash shows greatly superior performance to that obtainedfrom other sources heretofore available.

Fly ash made from bituminous coal is normally low in calcium and/ormagnesium oxide content. Such fly ash is well known to be a pozzolanwhereby the finely divided amorphous siliceous glass will react withcalcium and magnesium oxide (or hydroxides) to develop cementitiouscompounds. On the other hand, fly ash produced from the combustion oflignite coal is well known to contain substantial quantities of calciumoxide and magnesium oxide. However, the utilization of such an ash incompositions such as Portland cement mortar and concrete can producedeleterious expansive reactions due, it is believed, to the hydrationproducts produced when the oxide is cured over extended periods of timein the presence of moisture. An example of this type of reaction isdemonstrated in the inability of such lignite ashes to remaindimensionally stable when tested in a high pressure autoclave. When theCaO content exceeds a maximum (threshold) amount the deleteriousexpansion occurs.

In the case of the fly ash of this invention, concentrations of calciumand magnesium compounds are so high that serious expansion would beexpected. However, due to the formation of the complex sulfates and alsodue to the high concentration of sulfate ions, these deleteriousreactions do not occur. Furthermore, tests have shown that the complexsulfates cause a dramatic change in the hydraulicity of the fly ash whenused in compositions such as mortar, concrete, and road baseformulations.

The preferred method of making products according to this inventioninvolves the injection oflime into the boiler at a particulartemperature range under conditions that provide for reaction of themajor part of the lime with the sulfur oxide gases-in the presence ofsemimolten fly ash, thereby producing the product of the invention. Thelime may be quicklime or preferably hydrated lime. One excellent form oflime is a dolomitic hydrate of the formula:

(OH)z'MgO'xH O where x may be any value from 1 to 0.

In any event, the lime or limestone used in accordance with thisinvention can either be high calcium lime or limestone, or so-calleddolomitic lime or limestone containing a mixture of calcium andmagnesium oxides or carbonates. For purposes of this invention,magnesium oxide and calcium oxide are considered to be substantiallycompletely interchangeable.

The lime or limestone can either be introduced separately into thecombustion chamber of the boiler or can be interground with the coal toform a composite starting material which is then conducted into thefurnace in the conventional manner. The former is preferred.

While limestone, the carbonate, is often useful in accordance with aprocess according to this invention, it is preferred to premake the limein a conventional lime kiln or otherwise, eliminating all or asubstantial part of the carbonate content of the limestone, and then tointroduce the lime either as calcium oxide or magnesium oxide or amixture of the two into the coal furnace at the operating temperature ofthe combustion part of the furnace. This gives an extremely quickreaction between the sulfur content of the coal and the alkali metalcontent of the lime, and produces a reaction product which is extremelyeasy to handle and makes exceptionally good load-supporting material.

It is highly preferred according to this invention that the hydratedlime be made up of particles not exceeding about 5 microns in size andpreferably ofa size not to exceed about 1 micron. The surface area ofthe material is preferably of the order of about 30,000 sq. cm./g. orgreater. The preferred type of hydrate for the process is a specialmaterial produced from quicklime formed in the lime kiln described inU.S. Pat. No. 3,250,520 of Bolton L. Corson et al. Such a quicklime hasabnormally high reactivity and when converted to a hydrate demonstratessuperior features when utilized in the process of this invention.Furthermore, the production of a dihydrated dolomitic lime (such asdescribed in the U.S. Pat. No. 2,309,168 of Bolton L. Corson) has beenfound to be the most effective in carrying out the reaction in theboiler.

The reaction in the boiler is temperature limited and the injection ofthe lime material must be made at a point in the boiler where thetemperature is in the range of about l,500 to 2,000 F. Temperaturessubstantially below about 1,500 F. will not ordinarily result in asuitable reaction, particularly insofar as the magnesium oxide contentis concerned. Where high calcium material is used, or where themagnesium content is low, the temperature may be dropped several hundreddegrees with a reasonably satisfactory performance.

One other factor of importance is that the reactant material must bedispersed throughout the gases of combustion in the boiler in a mannerto provide intimate contact between the particles and the gas stream.This may be done by the use ofa mechanical injection device such as ahigh-speed screw, for example. One of the advantages of using the (lime)dihydrate is that it produces a thorough dispersion under thiscondition. The injection may also be accomplished by the use of air,combustion gases, or steam provided that the injection gas is not usedin an excessive amount which would cause instability within the boiler.

In accordance with the preferred process of manufacturing the highlyactive fly ash in accordance with this invention, coal is burned in anyexisting coal furnace, in the presence of sulfur which is eitherinitially present in the coal or has been added to the coal in the eventthat the original sulfur content of the coal is too low. This producesflue gases and fly ash in the furnace stack, such flue gases containingsulfur in gaseous form. In accordance with this invention, lime whichhas been previously prepared in a conventional lime kiln is injectedinto a boiler in an area of high temperatures such as l500-2000 F., forexample. The sulfur reacts quickly with the lime and with the oxygen inthe air to produce a dry fly ash product which has a high sulfatecontent, as previously discussed. This reaction product is a highlyreactive fly ash and makes extremely good load-supporting compositionsof the type referred to hereinafter. Further, the reaction product isdry and easy to handle, and to package and ship.

It is known that lime and fly ash produce agglomerates when they react,and that these agglomerates do not all enter into thestrength-developing sulfopozzolanic reaction. Conventional methods ofdispersing these ingredients do not work well, but it has been foundthat an intimate mixture which is surprisingly free of agglomerates canbe obtained by feeding lime or limestone into the high-temperatureportion of a conventional boiler, which not only reacts with the sulfurcontent in the fly ash in the boiler, but also causes reactions withglassy phases of the fly ash, and furthermore acts in such a way that itis substantially uniformly distributed in the fine particulate state,without the formation of disadvantageous agglomerates.

It is believed that the principal reactants of the lime and limestone ofthe strength-developing sulfopozzolanic reaction are calcium hydroxide,Ca(OH) calcium oxide, CaO, and magnesium oxide, MgO.

It is to be appreciated that, while most forms of coal are so low incalcium and magnesium content, such as calcium and magnesium carbonate,that no reaction of any substantial extent in accordance with thisinvention is achieved by using the original content of the coal alone.However, certain specific types of coal such as lignites have limestonesin them as they occur in nature, but lignites have low sulfur contentand it may be desirable to augment their sulfur content in order toachieve the highly desirable results that are attained in accordancewith this invention.

lt is not known why the fly ash according to this invention gives suchexcellent results in combination with lime and aggregate. However, it isknown that the sulfur enters into chemical (and perhaps other) reactionsat the high temperatures that exist in the furnace, believed to formcomplexes ofa nature not yet fully ascertained. It should sufflce to saythat the sulfur is not merely present as a mechanical mixture of calciumsulfate and magnesium sulfate with the other ingredients of the fly ash.lt is considered likely that an anhydrite of the calcium sulfoaluminatesubstance known as ettringrite" 3CaO'l O '3CaSO '30-32 H O is formed atleast in part, and that this may be partially responsible for theexcellent hydraulic set that is obtained when the high-sulfate fly ashaccording to this invention is combined with water and an aggregate.

It is believed that the excellence of the fly ash in accordance withthis invention is based at least in part on the fact that it is reactivewith water to produce from about 4 to 50 percent by weight based on theoriginal weight of the fly ash of alkali metal sulfoaluminate hydrateswhich appear in two forms, one of which is referred to as thehigh-sulfate form and the other as the low-sulfate form. Thehigh-sulfate form corresponds approximately to the formula 3MO-Al- O'3MSO.-30-32 H O, where M represents calcium or magnesium, and thecalcium form is known as ettringrite." The low-sulfate form correspondsapproximately to the formula 3MO-Al O -MS0; 12-l 3 H O. One or bothforms of alkali metal sulfoaluminate hydrate can be detected in finalcompositions that are produced according to this invention by electronmicroscopy procedures.

In accordance with this invention, particularly the reaction stageinvolving the reaction between the lime or limestone on the one hand andthe fly ash on the other, the preferred reaction temperature is aboutl,800 to about l900 F., at a reaction time which totals approximatelyl-3 seconds, ideally about 2 seconds. This differs drastically from thereaction temperatures and times that are obtained in Portland cementfurnaces, where the reaction products are formed at about 2,800" F., andthe reaction is permitted to continue for about 20-30 minutes.

lt has been found that the presence of the high-sulfate form of alkalimetal sulfoaluminate hydrate produces a structural product that isself-sealing to a considerable extent. The formation of alkali metalsulfoaluminate hydrate with 32 molecules of water is an expansivereaction, but the compound seals itself so that it has greatly reducedcapillarity and therefore has better resistance to the effects ofmoisture. Also, the resulting load-supporting composition, when exposedto the elements, has better resistance to alternate cycles of wettingand drying, which is a factor of great importance in the performance ofsuch load-supporting materials.

It is, of course, a salient advantage of this invention that, because ofthe relatively high-speed reactions that are achieved when using specialfly ash in accordance with this invention, load-supporting surfacescontaining the fly ash together with lime and soil can be mixed togetherin wet weather and compacted in place, particularly during relativelycool wet seasons such as the late fall season, for example, and thepozzolanic reactions still go forward with amazing speed to produce ahighly satisfactory load-supporting material. This is not the case inconnection with any other fly ash ofwhich I am aware.

It is to be appreciated that additives such as accelerators,decelerators, water reducers, and even Portland cement, gypsum, and thelike may be included in compositions in accordance with this invention.These sometimes serve to give better density and to improve otherproperties of the final composition.

The process in accordance with this invention is highly advantageouscommercially because it not only makes effective utilization of sulfurwhich is often considered an undesirable ingredient in coal but it alsodesulfurizes the stack gases of the furnace, thus eliminating a possiblesource of air pollution.

The proportions of ingredients in accordance with this invention arecritical. The following relative proportions are used in carrying outthe process:

Highly active fly ash 8-90 Aggregate 5-87 Water 5-30 The highly activefly ash according to this infomtation has a combined sulfur content ofabout 5 to 50 percent expressed as sulfur trioxide, and a content ofcalcium oxide plus magnesium oxide (actually present as these compounds)from about 0.5 percent to about 30 percent by weight, wherein the ratioof uncombined calcium oxide plus magnesium oxide to combined calciumoxide plus magnesium oxide varies from about 0.2:l to about 3:1.

The products in accordance with this invention have been subjected tomany series of tests in order to determine and to prove their improvedcharacteristics. The following compressive strength tests indicate thatin the early stages of development a strength as high as five times thestrength ofa normal mix can be obtained in accordance with thisinvention.

EXAMPLE I Apparatus 1. Several Plexiglas tubes 1 inch ID by 10 incheslong (open at both ends), capped at one end with a small piece of clothheld in place with a rubber band.

2. A penetration gauge which indicates the hydraulic pressure requiredto penetrate 1 inch into the material in question. Procedure I.Plexiglas tubes were loosely filled with each of several samples of thetwo types of fly ashesbituminous and highly active.

2. The tubes were placed-cloth-capped end down-in a large container.

3. Into the container was placed several inches of water whichimmediately began soaking up into the tubes; in a few minutes goingabove the water line by capillary action.

4. The specimens were given a penetration test 6 days after initialwetting.

Results Bituminous Highly Active EXAMPLE tt Apparatus 1. Several glasscylinders 2 inches ID by 5% inches long (open at both ends), capped atone end with a piece of nylon cloth held in place with a rubber band. 2.A penetration gauge designed to indicate the hydraulic pressure requiredto penetrate 1 inch into the specimen. The minimum discernable initialwetting. Results Specimen Pressure (p.s.i.) required to penetrate 1 inchinto the specimen Bituminous Fly Ash A 40 8 40 C 40 Highly Active FlyAsh A 600 B 3,000 C 8,000 D 1.600

Under certain conditions this invention is operative without includingany lime in the normal fly ash-lime-aggregate mixture. Frequently, itwill be found that there is sufficient residual calcium oxide ormagnesium oxide or a mixture of the two in this fly ash to perform thepozzolanic function of the lime in the final mixture.

The following tests have been conducted which show the sharply improvedresults that are obtained in accordance with this invention.

EXAMPLE "I Purpose To specifically clearly show the differences betweencompositions of aggregate, fly ash, and lime, using fly ashes of thebituminous and highly active categories, the following series of testswere run. Materials 1. Fly Ashes Chemical analysis and sieve fineness offly ash A (bituminous) in fly ash B (highly active) are shown in thefollowing table.

TABLE l4-l Test Fly Ash A Fly Ash 8 Normal Fly Ash Fly Ash from fromBituminous Coal Bituminous Coal, resulting from Dolomite additionChemical Analysis 1 SiO 39.6 24.7 k M 0, 23.9 [4.0 Z R 0 I29 Z (a0 6.322.0 i MgO 1.2 16.5 2 50 L5 6.0

Sieve Fineness It Through No. 325 89.3 83.6

2. Hydrated Lime In all tests described in this example a monohydrateddolomitic lime was used, the chemical formulation for this is calciumhydroxide plus magnesium oxide.

3. Aggregate For aggregate, graded Ottawa sand was used. This is acommon denominator for all laboratory tests of nonplastic lime/flyash/aggregate mixtures.

Procedure 1. The lime (if any), fly ash, and sand were dry-blended. Thewater requirement for these mixes is covered by ASTM method D l557-66T,title being Moisture Density Relation of Soils Using l lb. (Ten-pound)Rammer and 18-inch Drop. The purpose of this method is to develop themaximum compressibility or maximum density of the finished compactedspecimen. The mixing procedure used for forming the specimens is thatdesignated as C59366T whose title is Fly Ash and Other Pozzolans For UseWith Lime. This specification also covers the forming of the specimen.Specimens are formed in three layers, each layer receiving 25 uniformlydistributed blows from the lb. hammer dropped from a distance of ISinches, again as described in this ASTM specification.

Formed specimens are cylinders having a diameter of 4.0 inches and aheight of 4.6 inches. Specimens are placed in sealed containers andcured in a 100 F. oven for l4 days. After 14 days of curing thespecimens are broken by compression. the test results given below are inp.s.i. of the maximum load withstood by the specimen.

Test Results The following table indicates the results of the abovetesting for bituminous and highly active fly ashes in conjunction withvarying quantities of lime.

Specimens too weak for testing COMPRESSIVE STRENGTH OF ROAD BASEMATERIALS Type of Fly Ash Monohydrated Dolomitic Lime Normal fly ashfrom hituminuus coal I00 p.s.i. 342 psi. $65 p.s.i. Fly ash frombituminous coal, resulting from dolomite addition 553 p.s.i. 925 p.s.i.(s35 p.s.i.

' Using procedure ofpreceding example It has also been discovered thatsome forms of high-sulfur fly ash in accordance with this invention canthemselves stabilize soil without the addition of any lime. Fly ash inaccordance with this phase ofthe invention contains substantialquantities of calcium oxide, and has a composition within the rangesspecified below.

TYPICAL ANALYSIS OF HIGH-SULFUR FLY ASH Wet Analysis Fly Ash Moist CuredFly Ash 1 ignition loss L9 7.] '1 C L5 [.4 '1 5&0, 24.2 12.7 '1 Fe,('),|4.| r12 '1 Al,O 9.5 8.9 '1 (a0 ll.5 10.8 '1 MgO w 9.0

While this invention has been described with reference to many specificembodiments, it is to be understood that these examples are intended tobe illustrative and not to limit the scope of the invention, which scopeis defined in the appended claims. It should be emphasized that it isnot necessary to use the highly active sulfopozzolanically reactive flyash alone, but that it can be combined with other materials withoutdisadvantageous effects, provided those other materials do not interfere with the reactivity of the highly active ash. Examples ofmaterials that can be added are Portland cement, ordinary fly ash, andlime, either as oxide or hydroxide or mixtures of the two. It willfurther be appreciated that the term aggregate as used herein isintended to be a generic term and includes soil and sand as well asother well-known aggregates such as rock, crushed stone, cinders, andother well-known aggregates. Further, while the fly ash according tothis invention is preferably manufactured in dry form, and is so claimedherein, it will be appreciated that water may be added without departingfrom the scope of the claims. Indeed, water is a highly desirableadditive since its presence greatly enhances the speed of thesulfopozzolanic reaction, either when fly ash is used alone or incombination with other ingredients as disclosed herein.

The following is claimed:

1. A highly active, finely divided sulfopozzolanically reactivebituminous coal fly ash containing about 5 percent to about 50 percentby weight of combined sulfate expressed as 50;, and wherein the contentof alkali earth metal oxide is from about 0.5 percent to about 30percent by weight, and wherein the ratio of uncombined alkali earthmetal oxide to combined alkali earth metal oxide is in the range ofabout 0.2:l to about 3: l.

2. The fly ash of claim I, wherein the fly ash contains an alkali earthmetal selected from the group consisting of calcium and magnesium andmixtures thereof, and the sulfate is chemically combined with the alkaliearth metal.

3. The fly ash of claim 2, wherein the sulfate is present as alkaliearth metal sulfoaluminate.

4. The fly ash of claim 2, wherein the sulfate is present as a triplesalt including alkali earth metal oxide, A1 0 and CaSO bonded to oneanother.

5. The fly ash of claim 1, wherein the sulfate is present in a formwhich reacts with water to form 3MO'Al O -,'3MSO '30-3 ZHQO, where M isan alkali earth metal selected from the group consisting of calcium andmagnesium and mixtures thereof.

6. The fly ash of claim 1, where the sulfate is present in a form whichreacts with water to form 3MO'AI,O 'MSO 12-1 3H O, where M is an alkaliearth metal selected from the group consisting of calcium and magnesiumand mixtures thereof.

7. A material suitable for forming a stabilized load-supportingcomposition consisting essentially of about 8 to about percent by weightof highly active fly ash, and about 5 to about 92 percent by weight ofaggregate, said fly ash containing about 5 to about 50 percent by weightof a combined sulfate, expressed as 50;, based upon the weight of thefly ash.

8. the material defined in claim 7, wherein the fly ash contains analkali earth metal selected from the group consisting of calcium andmagnesium and mixtures thereof, and the sulfate is chemically combinedwith the alkali earth metal.

9. The material defined in claim 8, wherein the sulfate is present asalkali earth metal sulfoaluminate.

10. The material defined in claim 8, wherein the sulfate is present as atriple salt including alkali earth metal oxide, A1 0 and CaSO, bonded toone another.

II. The material defined in claim 8, wherein the sulfate is present in aform which reacts with water to form 3MO-Al O '3MSO -3032H O, where M isan alkali earth metal selected from the group consisting of calcium andmagnesium and mixtures thereof.

and mixtures thereof.

2. The fly ash of claim 1, wherein the fly ash contains an alkali earthmetal selected from the group consisting of calcium and magnesium andmixtures thereof, and the sulfate is chemically combined with the alkaliearth metal.
 3. The fly ash of claim 2, wherein the sulfate is presentas alkali earth metal sulfoaluminate.
 4. The fly ash of claim 2, whereinthe sulfate is present as a triple salt including alkali earth metaloxide, Al2O3 and CaSO4 bonded to one another.
 5. The fly ash of claim 1,wherein the sulfate is present in a form which reacts with water to form3MO.Al2O3.3MSO4.30-32H2O, where M is an alkali earth metal selected fromthe group consisting of calcium and magnesium and mixtures thereof. 6.The fly ash of claim 1, where the sulfate is present in a form whichreacts with water to form 3MO.Al2O3.MSO4.12-13H2O, where M is an alkaliearth metal selected from the group consisting of calcium and magnesiumand mixtures thereof.
 7. A material suitable for forming a stabilizedload-supporting composition consisting essentially of about 8 to about95 percent by weight of highly active fly ash, and about 5 to about 92percent by weight of aggregate, said fly ash containing about 5 to about50 percent by weight of a combined sulfate, expressed as SO3, based uponthe weight of the fly ash.
 8. the material defined in claim 7, whereinthe Fly ash contains an alkali earth metal selected from the groupconsisting of calcium and magnesium and mixtures thereof, and thesulfate is chemically combined with the alkali earth metal.
 9. Thematerial defined in claim 8, wherein the sulfate is present as alkaliearth metal sulfoaluminate.
 10. The material defined in claim 8, whereinthe sulfate is present as a triple salt including alkali earth metaloxide, Al2O3, and CaSO4 bonded to one another.
 11. The material definedin claim 8, wherein the sulfate is present in a form which reacts withwater to form 3MO.Al2O3.3MSO4.30-32H2O, where M is an alkali earth metalselected from the group consisting of calcium and magnesium and mixturesthereof.
 12. The material defined in claim 8, wherein the sulfate ispresent in a form which reacts with water to form 3MO.A12O3.MSO4.12-13H2O, where M is an alkali earth metal selected from the group consistingof calcium and magnesium and mixtures thereof.